Forwarding operations to bypass persistent memory

ABSTRACT

Techniques are provided for forwarding operations to bypass persistent memory. A modify operation, targeting an object, may be received at a persistent memory tier of a node. If a forwarding policy indicates that forwarding is not enabled for the modify operation and the target object, then the modify operation is executed through a persistent memory file system. If the forwarding policy indicates that forwarding is enabled for the modify operation and the target object, then the modify operation is forwarded to a file system tier as a forwarded operation for execution through a storage file system.

BACKGROUND

A node, such as a server, a computing device, a virtual machine, a cloudservice, etc., may host a storage operating system. The storageoperating system may be configured to store data on behalf of clientdevices, such as within volumes, aggregates, storage devices, cloudstorage, locally attached storage, etc. In this way, a client can issueread and write operations to the storage operating system of the node inorder to read data from storage or write data to the storage. Thestorage operating system may implement a storage file system throughwhich the data is organized and accessible to the client devices. Thestorage file system may be tailored for managing the storage and accessto data within a particular type of storage media, such asblock-addressable storage media of hard drives, solid state drives,and/or other storage. The storage media and the storage file system maybe managed by a file system tier of the node. The node may also compriseother types of storage media, such as persistent memory that providesrelatively lower latency compared to the storage media managed by thefile system tier. The persistent memory may be byte-addressable, and ismanaged by a persistent memory tier tailored for the performance andpersistence semantics of the persistent memory.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example computing environmentin which an embodiment of the invention may be implemented.

FIG. 2 is a block diagram illustrating an example of a networkenvironment with exemplary nodes in accordance with an embodiment of theinvention.

FIG. 3 is a block diagram illustrating an example of various componentsthat may be present within a node that may be used in accordance with anembodiment of the invention.

FIG. 4 is a block diagram illustrating an example of various componentsof system for implementing a persistent memory tier and a file systemtier in accordance with an embodiment of the invention.

FIG. 5 is a flow chart illustrating an example of a set of operationsthat support forwarding of operations to bypass persistent memory inaccordance with an embodiment of the invention.

FIG. 6 is a block diagram illustrating an example of supporting theforwarding of operations to bypass persistent memory in accordance withan embodiment of the invention.

FIG. 7 is a flow chart illustrating an example of a set of operationsthat support forwarding of operations to bypass persistent memory inaccordance with an embodiment of the invention.

FIG. 8 is a block diagram illustrating an example of supporting theforwarding of operations to bypass persistent memory in accordance withan embodiment of the invention.

FIG. 9 is a flow chart illustrating an example of a set of operationsthat support forwarding of operations to bypass persistent memory inaccordance with an embodiment of the invention.

FIG. 10A is a block diagram illustrating an example of supporting theforwarding of operations to bypass persistent memory in accordance withan embodiment of the invention.

FIG. 10B is a block diagram illustrating an example of supporting theforwarding of operations to bypass persistent memory in accordance withan embodiment of the invention.

FIG. 11 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

DETAILED DESCRIPTION

The techniques described herein are directed to the forwarding ofoperations to bypass persistent memory. A node may comprise a persistentmemory tier configured to store data within persistent memory through apersistent memory file system. The node may comprise a file system tierconfigured to store data within storage through a storage file system.The persistent memory may provide relatively lower latency compared tothe storage of the file system tier. Thus, certain data from the storageof the storage file system may be copied (tiered) into the persistentmemory in order to provide client devices with faster access to thecopied data through the persistent memory file system. The original datamay still be maintained within the storage of the storage file system.As modify operations are executed upon the persistent memory to changethe data within the persistent memory, the data within the persistentmemory may diverge from the original data within the storage of thestorage file system.

Because two instances of the tiered data of the frontend file system maybe stored across both the storage of the storage file system and thepersistent memory, an original instance of the tiered data within thestorage of the storage file system may become stale/old. The originalinstance of the tiered data may become stale because newer data may havebeen written to the tiered instance of the tiered data within thepersistent memory. To prevent stale data from being provided to clientsor operated upon, the node (e.g., file systems, operating systems, andservices of the node) may be configured to consider data within thepersistent memory as being the authoritative copy for any data blocksthat have been tiered to the persistent memory and are tracked by thepersistent memory file system. This configuration is referred to as aninvariant that is implemented so that client operations can be executedupon the persistent memory comprising the authoritative copy of data sothat clients are not accessing stale/old data. Processing the clientoperations using the persistent memory reduces the latency associatedwith processing the client operations due to the lower latencycharacteristics of the persistent memory. With this invariant, anyblocks of data that have been copied (tiered) into the persistent memoryand/or residing within the persistent memory will be the authoritativecopy of the data with respect to corresponding blocks within the storageof the storage file system.

Processing the client operations using the persistent memory reduces thelatency associated with processing the client operations due to thelower latency characteristics of the persistent memory. At a subsequentpoint in time, a framing process may be performed to identify moreup-to-date data within the persistent memory compared to correspondingdata in the storage of the storage file system. For example, the framingprocess may evaluate modify timestamps of data blocks to identify datablocks that have been modified since a last framing process. In anotherexample, write operations may set flags for data blocks when new data iswritten to the data blocks, and thus the flags may indicate that thedata blocks comprise the more up-to-date data. In this way, the framingprocess may be performed where the persistent memory tier notifies thefile system tier that more up-to-date data is stored within thepersistent memory compared to what is stored within the storage by thestorage file system of the file system tier. In this way, the filesystem tier can refer to and/or retrieve the more up-to-date data fromthe persistent memory for storage into the storage of the storage filesystem.

Certain types of operations may be better suited for being executedthrough the storage file system upon the storage as opposed to beingexecuted through the persistent memory file system upon the persistentmemory. In some embodiments, certain operations may be identified asbeing inefficient to execute through the persistent memory file system,such as multi-block sequential write operations, partial writeoperations, hole punch operations, etc., which would be more efficientto execute through the storage file system upon the storage and/oroperations targeted data blocks not tiered to the persistent memory.Accordingly, as provided herein, these operations may bypass executionby the persistent memory file system, and may be forwarded to thestorage file system as forwarded operations for execution through thestorage file system upon the storage.

The forwarding of operations are performed in manner that preserves theinvariant that the authoritative copy of data is maintained in thepersistent memory by removing data from the persistent memory that hasbecome stale due to the forwarding. Otherwise, clients may be servedstale data and/or file system inconsistencies between the storage filesystem and the persistent memory file system may result. To ensure thatstale data is not stored within the persistent memory, when forwardingan operation to write new data to a block within the storage of thestorage file system, a stale copy of the data is removed from acorresponding block in the persistent memory. The removal of the stalecopy of the data from the persistent memory may be performed prior tothe operation being forwarded to the storage file system or after thenew data has been written to the storage of the storage file system.

In some embodiments, forwarding of modify operations may be performedduring framing so that a framing backlog of blocks having moreup-to-date data within the persistent memory is not growing due toincoming modify operations otherwise being executed upon the persistentmemory. But, since the modify operations are being forwarded and arebypassing the persistent memory, the framing backlog is not growing.Framing is performed by the persistent memory tier to notify the filesystem tier of blocks within the persistent memory that comprise moreup-to-date data than corresponding blocks in the storage of the storagefile system.

During framing, if incoming modify operations continue to be executedagainst the persistent memory to write new data to the persistentmemory, then the framing backlog of blocks, having more up-to-date data,that are to be identified and indicated to the file system tier willcontinue to grow, thus hindering the ability for the framing process tocomplete. In this way, these modify operations are instead forwarded tothe storage file system, and bypass the persistent memory file system sothat the framing backlog is not increasing. In some embodiments,forwarding may be implemented for other use cases, such as during thecreation of a snapshot of data stored across the storage file system andthe persistent memory file system, the creation of file clones, holepunching to make unused blocks of data available to store new data,partial write operations targeting less than a full block of data (e.g.,less than a 4 kb block of data), etc.

Forwarding has various interactions with other storage functions, andthus forwarding of operations are performed in a manner that maintainsconsistency of the file systems and ensures clients are not served withstale data due to these interactions between forwarding and the otherstorage functions. In some embodiments, forwarding may be performed inmanner that addresses race situations between forwarded operations andframing operations. For example, if a forwarded operation and a pendingframing operation target a same object, then the forwarded operation andthe pending framing operation are synchronized by either suspending theforwarded operation or causing the pending framing operation to skip theobject based upon an internal state of the object (e.g., a stateindicating progress of the object being stored/flushed to persistentmemory) and/or other conditions.

Additionally, forwarding may be performed during a consistency pointoperation and/or a log replay operation in a manner that enforces filesystem correctness. For example, when a forwarded operation isimplemented to write new data to the storage of the storage file systemand remove the stale data from the persistent memory of the node, aremote direct memory access transfer is implemented to notify a partnernode of the changes. In this way, the partner node can mirror thechanges to local persistent memory and/or storage so that the partnernode maintains a mirrored copy of data stored by the node, which can beused for data redundancy and failover purposes.

A consistency point operation is blocked from being implemented untilall pending remote direct memory access transfers are complete. Thisensures consistency between the node and the partner node. In an exampleof ensuring consistency when replaying forwarded operations within a logduring a takeover process for a failed node, the partner node may mirroroperations to the node, and the node may log the operations into a log.If the partner node fails, then the node will replay the log andtakeover the processing of client operations in place of the failedpartner node. During replay, framing operations that target blocks withunknown states are replayed (e.g., blocks that are not part of thepersistent memory file system, and are merely tracked by the storagefile system), while framing operations that target blocks with knownstates are skipped (e.g., blocks that are tracked and owned by thepersistent memory file system, and are thus deemed to comprise theauthoritative copy of data due the invariant).

Various embodiments of the present technology provide for a wide rangeof technical effects, advantages, and/or improvements to computingsystems and components. For example, various embodiments may include oneor more of the following technical effects, advantages, and/orimprovements: 1) the ability to forward certain operations to a storagefile system and bypass a persistent memory file system because theseoperations are more efficient, less complex, and faster to executethrough the storage file system; 2) implementing forwarding in order toprovide the ability to create snapshots, file clones, perform holepunching, and implement partial writes for a storage system implementingboth a storage file system and a persistent memory file system; 3)preserving an invariant that persistent memory is to have theauthoritative copy of data notwithstanding operations bypassing thepersistent memory file system during forwarding, which ensures filesystem consistency and ensures that stale data is not served to clients;4) the ability to ensure file system consistency and user dataconsistency when forwarding is implemented during framing bysynchronizing forwarded operations and pending framing operations; 5)the ability to perform a consistency point to accept and store (flush)modifications to a storage device while keeping data consistent betweenthe node and a partner node; and 6) the ability to selectively replayoperations within a log (an NVLog) during a failover situation withoutdata loss and without placing the persistent memory file system in anincorrect state.

FIG. 1 is a diagram illustrating an example operating environment 100 inwhich an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 128, such as a laptop, a tablet, apersonal computer, a mobile device, a server, a virtual machine, awearable device, etc. In another example, the techniques describedherein may be implemented within one or more nodes, such as a first node130 and/or a second node 132 within a first cluster 134, a third node136 within a second cluster 138, etc., which may be part of aon-premise, cloud-based, or hybrid storage solution.

A node may comprise a storage controller, a server, an on-premisedevice, a virtual machine such as a storage virtual machine, hardware,software, or combination thereof. The one or more nodes may beconfigured to manage the storage and access to data on behalf of theclient device 128 and/or other client devices. In another example, thetechniques described herein may be implemented within a distributedcomputing platform 102 such as a cloud computing environment (e.g., acloud storage environment, a multi-tenant platform, a hyperscaleinfrastructure comprising scalable server architectures and virtualnetworking, etc.) configured to manage the storage and access to data onbehalf of client devices and/or nodes.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 128, the one ormore nodes 130, 132, and/or 136, and/or the distributed computingplatform 102. For example, the client device 128 may transmitoperations, such as data operations to read data and write data andmetadata operations (e.g., a create file operation, a rename directoryoperation, a resize operation, a set attribute operation, etc.), over anetwork 126 to the first node 130 for implementation by the first node130 upon storage.

The first node 130 may store data associated with the operations withinvolumes or other data objects/structures hosted within locally attachedstorage, remote storage hosted by other computing devices accessibleover the network 126, storage provided by the distributed computingplatform 102, etc. The first node 130 may replicate the data and/or theoperations to other computing devices, such as to the second node 132,the third node 136, a storage virtual machine executing within thedistributed computing platform 102, etc., so that one or more replicasof the data are maintained. For example, the third node 136 may host adestination storage volume that is maintained as a replica of a sourcestorage volume of the first node 130. Such replicas can be used fordisaster recovery and failover.

In an embodiment, the techniques described herein are implemented by astorage operating system or are implemented by a separate module thatinteracts with the storage operating system. The storage operatingsystem may be hosted by the client device, 128, a node, the distributedcomputing platform 102, or across a combination thereof. In someembodiments, the storage operating system may execute within a storagevirtual machine, a hyperscaler, or other computing environment. Thestorage operating system may implement a storage file system tologically organize data within storage devices as one or more storageobjects and provide a logical/virtual representation of how the storageobjects are organized on the storage devices.

A storage object may comprise any logically definable storage elementstored by the storage operating system (e.g., a volume stored by thefirst node 130, a cloud object stored by the distributed computingplatform 102, etc.). Each storage object may be associated with a uniqueidentifier that uniquely identifies the storage object. For example, avolume may be associated with a volume identifier uniquely identifyingthat volume from other volumes. The storage operating system alsomanages client access to the storage objects.

The storage operating system may implement a file system for logicallyorganizing data. For example, the storage operating system may implementa write anywhere file layout for a volume where modified data for a filemay be written to any available location as opposed to a write-in-placearchitecture where modified data is written to the original location,thereby overwriting the previous data. In some embodiments, the filesystem may be implemented through a file system layer that stores dataof the storage objects in an on-disk format representation that isblock-based (e.g., data is stored within 4 kilobyte blocks and inodesare used to identify files and file attributes such as creation time,access permissions, size and block location, etc.).

Deduplication may be implemented by a deduplication module associatedwith the storage operating system. Deduplication is performed to improvestorage efficiency. One type of deduplication is inline deduplicationthat ensures blocks are deduplicated before being written to a storagedevice. Inline deduplication uses a data structure, such as an incorehash store, which maps fingerprints of data to data blocks of thestorage device storing the data. Whenever data is to be written to thestorage device, a fingerprint of that data is calculated and the datastructure is looked up using the fingerprint to find duplicates (e.g.,potentially duplicate data already stored within the storage device). Ifduplicate data is found, then the duplicate data is loaded from thestorage device and a byte by byte comparison may be performed to ensurethat the duplicate data is an actual duplicate of the data to be writtento the storage device. If the data to be written is a duplicate of theloaded duplicate data, then the data to be written to disk is notredundantly stored to the storage device.

Instead, a pointer or other reference is stored in the storage device inplace of the data to be written to the storage device. The pointerpoints to the duplicate data already stored in the storage device. Areference count for the data may be incremented to indicate that thepointer now references the data. If at some point the pointer no longerreferences the data (e.g., the deduplicated data is deleted and thus nolonger references the data in the storage device), then the referencecount is decremented. In this way, inline deduplication is able todeduplicate data before the data is written to disk. This improves thestorage efficiency of the storage device.

Background deduplication is another type of deduplication thatdeduplicates data already written to a storage device. Various types ofbackground deduplication may be implemented. In an embodiment ofbackground deduplication, data blocks that are duplicated between filesare rearranged within storage units such that one copy of the dataoccupies physical storage. References to the single copy can be insertedinto a file system structure such that all files or containers thatcontain the data refer to the same instance of the data.

Deduplication can be performed on a data storage device block basis. Inan embodiment, data blocks on a storage device can be identified using aphysical volume block number. The physical volume block number uniquelyidentifies a particular block on the storage device. Additionally,blocks within a file can be identified by a file block number. The fileblock number is a logical block number that indicates the logicalposition of a block within a file relative to other blocks in the file.For example, file block number 0 represents the first block of a file,file block number 1 represents the second block, and the like. Fileblock numbers can be mapped to a physical volume block number that isthe actual data block on the storage device. During deduplicationoperations, blocks in a file that contain the same data are deduplicatedby mapping the file block number for the block to the same physicalvolume block number, and maintaining a reference count of the number offile block numbers that map to the physical volume block number.

For example, assume that file block number 0 and file block number 5 ofa file contain the same data, while file block numbers 1-4 containunique data. File block numbers 1-4 are mapped to different physicalvolume block numbers. File block number 0 and file block number 5 may bemapped to the same physical volume block number, thereby reducingstorage requirements for the file. Similarly, blocks in different filesthat contain the same data can be mapped to the same physical volumeblock number. For example, if file block number 0 of file A contains thesame data as file block number 3 of file B, file block number 0 of fileA may be mapped to the same physical volume block number as file blocknumber 3 of file B.

In another example of background deduplication, a changelog is utilizedto track blocks that are written to the storage device. Backgrounddeduplication also maintains a fingerprint database (e.g., a flatmetafile) that tracks all unique block data such as by tracking afingerprint and other filesystem metadata associated with block data.Background deduplication can be periodically executed or triggered basedupon an event such as when the changelog fills beyond a threshold. Aspart of background deduplication, data in both the changelog and thefingerprint database is sorted based upon fingerprints. This ensuresthat all duplicates are sorted next to each other. The duplicates aremoved to a dup file.

The unique changelog entries are moved to the fingerprint database,which will serve as duplicate data for a next deduplication operation.In order to optimize certain filesystem operations needed to deduplicatea block, duplicate records in the dup file are sorted in certainfilesystem sematic order (e.g., inode number and block number). Next,the duplicate data is loaded from the storage device and a whole blockbyte by byte comparison is performed to make sure duplicate data is anactual duplicate of the data to be written to the storage device. After,the block in the changelog is modified to point directly to theduplicate data as opposed to redundantly storing data of the block.

In some embodiments, deduplication operations performed by a datadeduplication layer of a node can be leveraged for use on another nodeduring data replication operations. For example, the first node 130 mayperform deduplication operations to provide for storage efficiency withrespect to data stored on a storage volume. The benefit of thededuplication operations performed on first node 130 can be provided tothe second node 132 with respect to the data on first node 130 that isreplicated to the second node 132. In some embodiments, a data transferprotocol, referred to as the LRSE (Logical Replication for StorageEfficiency) protocol, can be used as part of replicating consistencygroup differences from the first node 130 to the second node 132.

In the LRSE protocol, the second node 132 maintains a history bufferthat keeps track of data blocks that the second node 132 has previouslyreceived. The history buffer tracks the physical volume block numbersand file block numbers associated with the data blocks that have beentransferred from first node 130 to the second node 132. A request can bemade of the first node 130 to not transfer blocks that have already beentransferred. Thus, the second node 132 can receive deduplicated datafrom the first node 130, and will not need to perform deduplicationoperations on the deduplicated data replicated from first node 130.

In an embodiment, the first node 130 may preserve deduplication of datathat is transmitted from first node 130 to the distributed computingplatform 102. For example, the first node 130 may create an objectcomprising deduplicated data. The object is transmitted from the firstnode 130 to the distributed computing platform 102 for storage. In thisway, the object within the distributed computing platform 102 maintainsthe data in a deduplicated state. Furthermore, deduplication may bepreserved when deduplicated data is transmitted/replicated/mirroredbetween the client device 128, the first node 130, the distributedcomputing platform 102, and/or other nodes or devices.

In an embodiment, compression may be implemented by a compression moduleassociated with the storage operating system. The compression module mayutilize various types of compression techniques to replace longersequences of data (e.g., frequently occurring and/or redundantsequences) with shorter sequences, such as by using Huffman coding,arithmetic coding, compression dictionaries, etc. For example, anuncompressed portion of a file may comprise “ggggnnnnnnqqqqqqqqqq”,which is compressed to become “4g6n10q”. In this way, the size of thefile can be reduced to improve storage efficiency. Compression may beimplemented for compression groups. A compression group may correspondto a compressed group of blocks. The compression group may berepresented by virtual volume block numbers. The compression group maycomprise contiguous or non-contiguous blocks.

Compression may be preserved when compressed data istransmitted/replicated/mirrored between the client device 128, a node,the distributed computing platform 102, and/or other nodes or devices.For example, an object may be created by the first node 130 to comprisecompressed data. The object is transmitted from the first node 130 tothe distributed computing platform 102 for storage. In this way, theobject within the distributed computing platform 102 maintains the datain a compressed state.

In an embodiment, various types of synchronization may be implemented bya synchronization module associated with the storage operating system.In an embodiment, synchronous replication may be implemented, such asbetween the first node 130 and the second node 132. It may beappreciated that the synchronization module may implement synchronousreplication between any devices within the operating environment 100,such as between the first node 130 of the first cluster 134 and thethird node 136 of the second cluster 138 and/or between a node of acluster and an instance of a node or virtual machine in the distributedcomputing platform 102.

As an example, during synchronous replication, the first node 130 mayreceive a write operation from the client device 128. The writeoperation may target a file stored within a volume managed by the firstnode 130. The first node 130 replicates the write operation to create areplicated write operation. The first node 130 locally implements thewrite operation upon the file within the volume. The first node 130 alsotransmits the replicated write operation to a synchronous replicationtarget, such as the second node 132 that maintains a replica volume as areplica of the volume maintained by the first node 130. The second node132 will execute the replicated write operation upon the replica volumeso that file within the volume and the replica volume comprises the samedata. After, the second node 132 will transmit a success message to thefirst node 130. With synchronous replication, the first node 130 doesnot respond with a success message to the client device 128 for thewrite operation until both the write operation is executed upon thevolume and the first node 130 receives the success message that thesecond node 132 executed the replicated write operation upon the replicavolume.

In another example, asynchronous replication may be implemented, such asbetween the first node 130 and the third node 136. It may be appreciatedthat the synchronization module may implement asynchronous replicationbetween any devices within the operating environment 100, such asbetween the first node 130 of the first cluster 134 and the distributedcomputing platform 102. In an embodiment, the first node 130 mayestablish an asynchronous replication relationship with the third node136. The first node 130 may capture a baseline snapshot of a firstvolume as a point in time representation of the first volume. The firstnode 130 may utilize the baseline snapshot to perform a baselinetransfer of the data within the first volume to the third node 136 inorder to create a second volume within the third node 136 comprisingdata of the first volume as of the point in time at which the baselinesnapshot was created.

After the baseline transfer, the first node 130 may subsequently createsnapshots of the first volume over time. As part of asynchronousreplication, an incremental transfer is performed between the firstvolume and the second volume. In particular, a snapshot of the firstvolume is created. The snapshot is compared with a prior snapshot thatwas previously used to perform the last asynchronous transfer (e.g., thebaseline transfer or a prior incremental transfer) of data to identify adifference in data of the first volume between the snapshot and theprior snapshot (e.g., changes to the first volume since the lastasynchronous transfer). Accordingly, the difference in data isincrementally transferred from the first volume to the second volume. Inthis way, the second volume will comprise the same data as the firstvolume as of the point in time when the snapshot was created forperforming the incremental transfer. It may be appreciated that othertypes of replication may be implemented, such as semi-sync replication.

In an embodiment, the first node 130 may store data or a portion thereofwithin storage hosted by the distributed computing platform 102 bytransmitting the data within objects to the distributed computingplatform 102. In one example, the first node 130 may locally storefrequently accessed data within locally attached storage. Lessfrequently accessed data may be transmitted to the distributed computingplatform 102 for storage within a data storage tier 108. The datastorage tier 108 may store data within a service data store 120, and maystore client specific data within client data stores assigned to suchclients such as a client (1) data store 122 used to store data of aclient (1) and a client (N) data store 124 used to store data of aclient (N). The data stores may be physical storage devices or may bedefined as logical storage, such as a virtual volume, LUNs, or otherlogical organizations of data that can be defined across one or morephysical storage devices. In another example, the first node 130transmits and stores all client data to the distributed computingplatform 102. In yet another example, the client device 128 transmitsand stores the data directly to the distributed computing platform 102without the use of the first node 130.

The management of storage and access to data can be performed by one ormore storage virtual machines (SVMs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 128,within the first node 130, or within the distributed computing platform102 such as by the application server tier 106. In another example, oneor more SVMs may be hosted across one or more of the client device 128,the first node 130, and the distributed computing platform 102. The oneor more SVMs may host instances of the storage operating system.

In an embodiment, the storage operating system may be implemented forthe distributed computing platform 102. The storage operating system mayallow client devices to access data stored within the distributedcomputing platform 102 using various types of protocols, such as aNetwork File System (NFS) protocol, a Server Message Block (SMB)protocol and Common Internet File System (CIFS), and Internet SmallComputer Systems Interface (iSCSI), and/or other protocols. The storageoperating system may provide various storage services, such as disasterrecovery (e.g., the ability to non-disruptively transition clientdevices from accessing a primary node that has failed to a secondarynode that is taking over for the failed primary node), backup andarchive function, replication such as asynchronous and/or synchronousreplication, deduplication, compression, high availability storage,cloning functionality (e.g., the ability to clone a volume, such as aspace efficient flex clone), snapshot functionality (e.g., the abilityto create snapshots and restore data from snapshots), data tiering(e.g., migrating infrequently accessed data to slower/cheaper storage),encryption, managing storage across various platforms such as betweenon-premise storage systems and multiple cloud systems, etc.

In one example of the distributed computing platform 102, one or moreSVMs may be hosted by the application server tier 106. For example, aserver (1) 116 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 122. Thus, an SVM executingon the server (1) 116 may receive data and/or operations from the clientdevice 128 and/or the first node 130 over the network 126. The SVMexecutes a storage application and/or an instance of the storageoperating system to process the operations and/or store the data withinthe client (1) data store 122. The SVM may transmit a response back tothe client device 128 and/or the first node 130 over the network 126,such as a success message or an error message. In this way, theapplication server tier 106 may host SVMs, services, and/or otherstorage applications using the server (1) 116, the server (N) 118, etc.

A user interface tier 104 of the distributed computing platform 102 mayprovide the client device 128 and/or the first node 130 with access touser interfaces associated with the storage and access of data and/orother services provided by the distributed computing platform 102. In anembodiment, a service user interface 110 may be accessible from thedistributed computing platform 102 for accessing services subscribed toby clients and/or nodes, such as data replication services, applicationhosting services, data security services, human resource services,warehouse tracking services, accounting services, etc. For example,client user interfaces may be provided to corresponding clients, such asa client (1) user interface 112, a client (N) user interface 114, etc.The client (1) can access various services and resources subscribed toby the client (1) through the client (1) user interface 112, such asaccess to a web service, a development environment, a human resourceapplication, a warehouse tracking application, and/or other services andresources provided by the application server tier 106, which may usedata stored within the data storage tier 108.

The client device 128 and/or the first node 130 may subscribe to certaintypes and amounts of services and resources provided by the distributedcomputing platform 102. For example, the client device 128 may establisha subscription to have access to three virtual machines, a certainamount of storage, a certain type/amount of data redundancy, a certaintype/amount of data security, certain service level agreements (SLAs)and service level objectives (SLOs), latency guarantees, bandwidthguarantees, access to execute or host certain applications, etc.Similarly, the first node 130 can establish a subscription to haveaccess to certain services and resources of the distributed computingplatform 102.

As shown, a variety of clients, such as the client device 128 and thefirst node 130, incorporating and/or incorporated into a variety ofcomputing devices may communicate with the distributed computingplatform 102 through one or more networks, such as the network 126. Forexample, a client may incorporate and/or be incorporated into a clientapplication (e.g., software) implemented at least in part by one or moreof the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, nodes,laptop computers, notebook computers, tablet computers or personaldigital assistants (PDAs), smart phones, cell phones, and consumerelectronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 102, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 104, theapplication server tier 106, and a data storage tier 108. The userinterface tier 104 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 110 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements(e.g., as discussed above), which may be accessed via one or more APIs.

The service user interface 110 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 102, such asaccessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 108 may include one or more data stores, which mayinclude the service data store 120 and one or more client data stores122-124. Each client data store may contain tenant-specific data that isused as part of providing a range of tenant-specific business andstorage services or functions, including but not limited to ERP, CRM,eCommerce, Human Resources management, payroll, storage services, etc.Data stores may be implemented with any suitable data storagetechnology, including structured query language (SQL) based relationaldatabase management systems (RDBMS), file systems hosted by operatingsystems, object storage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 102 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness-related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

A clustered network environment 200 that may implement one or moreaspects of the techniques described and illustrated herein is shown inFIG. 2 . The clustered network environment 200 includes data storageapparatuses 202(1)-202(n) that are coupled over a cluster or clusterfabric 204 that includes one or more communication network(s) andfacilitates communication between the data storage apparatuses202(1)-202(n) (and one or more modules, components, etc. therein, suchas, nodes 206(1)-206(n), for example), although any number of otherelements or components can also be included in the clustered networkenvironment 200 in other examples. This technology provides a number ofadvantages including methods, non-transitory computer readable media,and computing devices that implement the techniques described herein.

In this example, nodes 206(1)-206(n) can be primary or local storagecontrollers or secondary or remote storage controllers that provideclient devices 208(1)-208(n) with access to data stored within datastorage devices 210(1)-210(n) and cloud storage device(s) 236 (alsoreferred to as cloud storage node(s)). The nodes 206(1)-206(n) may beimplemented as hardware, software (e.g., a storage virtual machine), orcombination thereof.

The data storage apparatuses 202(1)-202(n) and/or nodes 206(1)-206(n) ofthe examples described and illustrated herein are not limited to anyparticular geographic areas and can be clustered locally and/or remotelyvia a cloud network, or not clustered in other examples. Thus, in oneexample the data storage apparatuses 202(1)-202(n) and/or node computingdevice 206(1)-206(n) can be distributed over a plurality of storagesystems located in a plurality of geographic locations (e.g., locatedon-premise, located within a cloud computing environment, etc.); whilein another example a clustered network can include data storageapparatuses 202(1)-202(n) and/or node computing device 206(1)-206(n)residing in a same geographic location (e.g., in a single on-site rack).

In the illustrated example, one or more of the client devices208(1)-208(n), which may be, for example, personal computers (PCs),computing devices used for storage (e.g., storage servers), or othercomputers or peripheral devices, are coupled to the respective datastorage apparatuses 202(1)-202(n) by network connections 212(1)-212(n).Network connections 212(1)-212(n) may include a local area network (LAN)or wide area network (WAN) (i.e., a cloud network), for example, thatutilize TCP/IP and/or one or more Network Attached Storage (NAS)protocols, such as a Common Internet Filesystem (CIFS) protocol or aNetwork Filesystem (NFS) protocol to exchange data packets, a StorageArea Network (SAN) protocol, such as Small Computer System Interface(SCSI) or Fiber Channel Protocol (FCP), an object protocol, such assimple storage service (S3), and/or non-volatile memory express (NVMe),for example.

Illustratively, the client devices 208(1)-208(n) may be general-purposecomputers running applications and may interact with the data storageapparatuses 202(1)-202(n) using a client/server model for exchange ofinformation. That is, the client devices 208(1)-208(n) may request datafrom the data storage apparatuses 202(1)-202(n) (e.g., data on one ofthe data storage devices 210(1)-210(n) managed by a network storagecontroller configured to process I/O commands issued by the clientdevices 208(1)-208(n)), and the data storage apparatuses 202(1)-202(n)may return results of the request to the client devices 208(1)-208(n)via the network connections 212(1)-212(n).

The nodes 206(1)-206(n) of the data storage apparatuses 202(1)-202(n)can include network or host nodes that are interconnected as a clusterto provide data storage and management services, such as to anenterprise having remote locations, cloud storage (e.g., a storageendpoint may be stored within cloud storage device(s) 236), etc., forexample. Such nodes 206(1)-206(n) can be attached to the cluster fabric204 at a connection point, redistribution point, or communicationendpoint, for example. One or more of the nodes 206(1)-206(n) may becapable of sending, receiving, and/or forwarding information over anetwork communications channel, and could comprise any type of devicethat meets any or all of these criteria.

In an embodiment, the nodes 206(1) and 206(n) may be configuredaccording to a disaster recovery configuration whereby a surviving nodeprovides switchover access to the data storage devices 210(1)-210(n) inthe event a disaster occurs at a disaster storage site (e.g., the nodecomputing device 206(1) provides client device 212(n) with switchoverdata access to data storage devices 210(n) in the event a disasteroccurs at the second storage site). In other examples, the nodecomputing device 206(n) can be configured according to an archivalconfiguration and/or the nodes 206(1)-206(n) can be configured based onanother type of replication arrangement (e.g., to facilitate loadsharing). Additionally, while two nodes are illustrated in FIG. 2 , anynumber of nodes or data storage apparatuses can be included in otherexamples in other types of configurations or arrangements.

As illustrated in the clustered network environment 200, nodes206(1)-206(n) can include various functional components that coordinateto provide a distributed storage architecture. For example, the nodes206(1)-206(n) can include network modules 214(1)-214(n) and disk modules216(1)-216(n). Network modules 214(1)-214(n) can be configured to allowthe nodes 206(1)-206(n) (e.g., network storage controllers) to connectwith client devices 208(1)-208(n) over the storage network connections212(1)-212(n), for example, allowing the client devices 208(1)-208(n) toaccess data stored in the clustered network environment 200.

Further, the network modules 214(1)-214(n) can provide connections withone or more other components through the cluster fabric 204. Forexample, the network module 214(1) of node computing device 206(1) canaccess the data storage device 210(n) by sending a request via thecluster fabric 204 through the disk module 216(n) of node computingdevice 206(n) when the node computing device 206(n) is available.Alternatively, when the node computing device 206(n) fails, the networkmodule 214(1) of node computing device 206(1) can access the datastorage device 210(n) directly via the cluster fabric 204. The clusterfabric 204 can include one or more local and/or wide area computingnetworks (i.e., cloud networks) embodied as Infiniband, Fibre Channel(FC), or Ethernet networks, for example, although other types ofnetworks supporting other protocols can also be used.

Disk modules 216(1)-216(n) can be configured to connect data storagedevices 210(1)-210(n), such as disks or arrays of disks, SSDs, flashmemory, or some other form of data storage, to the nodes 206(1)-206(n).Often, disk modules 216(1)-216(n) communicate with the data storagedevices 210(1)-210(n) according to the SAN protocol, such as SCSI orFCP, for example, although other protocols can also be used. Thus, asseen from an operating system on nodes 206(1)-206(n), the data storagedevices 210(1)-210(n) can appear as locally attached. In this manner,different nodes 206(1)-206(n), etc. may access data blocks, files, orobjects through the operating system, rather than expressly requestingabstract files.

While the clustered network environment 200 illustrates an equal numberof network modules 214(1)-214(n) and disk modules 216(1)-216(n), otherexamples may include a differing number of these modules. For example,there may be a plurality of network and disk modules interconnected in acluster that do not have a one-to-one correspondence between the networkand disk modules. That is, different nodes can have a different numberof network and disk modules, and the same node computing device can havea different number of network modules than disk modules.

Further, one or more of the client devices 208(1)-208(n) can benetworked with the nodes 206(1)-206(n) in the cluster, over the storageconnections 212(1)-212(n). As an example, respective client devices208(1)-208(n) that are networked to a cluster may request services(e.g., exchanging of information in the form of data packets) of nodes206(1)-206(n) in the cluster, and the nodes 206(1)-206(n) can returnresults of the requested services to the client devices 208(1)-208(n).In one example, the client devices 208(1)-208(n) can exchangeinformation with the network modules 214(1)-214(n) residing in the nodes206(1)-206(n) (e.g., network hosts) in the data storage apparatuses202(1)-202(n).

In one example, the storage apparatuses 202(1)-202(n) host aggregatescorresponding to physical local and remote data storage devices, such aslocal flash or disk storage in the data storage devices 210(1)-210(n),for example. One or more of the data storage devices 210(1)-210(n) caninclude mass storage devices, such as disks of a disk array. The disksmay comprise any type of mass storage devices, including but not limitedto magnetic disk drives, flash memory, and any other similar mediaadapted to store information, including, for example, data and/or parityinformation.

The aggregates include volumes 218(1)-218(n) in this example, althoughany number of volumes can be included in the aggregates. The volumes218(1)-218(n) are virtual data stores or storage objects that define anarrangement of storage and one or more filesystems within the clusterednetwork environment 200. Volumes 218(1)-218(n) can span a portion of adisk or other storage device, a collection of disks, or portions ofdisks, for example, and typically define an overall logical arrangementof data storage. In one example, volumes 218(1)-218(n) can includestored user data as one or more files, blocks, or objects that mayreside in a hierarchical directory structure within the volumes218(1)-218(n).

Volumes 218(1)-218(n) are typically configured in formats that may beassociated with particular storage systems, and respective volumeformats typically comprise features that provide functionality to thevolumes 218(1)-218(n), such as providing the ability for volumes218(1)-218(n) to form clusters, among other functionality. Optionally,one or more of the volumes 218(1)-218(n) can be in composite aggregatesand can extend between one or more of the data storage devices210(1)-210(n) and one or more of the cloud storage device(s) 236 toprovide tiered storage, for example, and other arrangements can also beused in other examples.

In one example, to facilitate access to data stored on the disks orother structures of the data storage devices 210(1)-210(n), a filesystemmay be implemented that logically organizes the information as ahierarchical structure of directories and files. In this example,respective files may be implemented as a set of disk blocks of aparticular size that are configured to store information, whereasdirectories may be implemented as specially formatted files in whichinformation about other files and directories are stored.

Data can be stored as files or objects within a physical volume and/or avirtual volume, which can be associated with respective volumeidentifiers. The physical volumes correspond to at least a portion ofphysical storage devices, such as the data storage devices 210(1)-210(n)(e.g., a Redundant Array of Independent (or Inexpensive) Disks (RAIDsystem)) whose address, addressable space, location, etc. does notchange. Typically, the location of the physical volumes does not changein that the range of addresses used to access it generally remainsconstant.

Virtual volumes, in contrast, can be stored over an aggregate ofdisparate portions of different physical storage devices. Virtualvolumes may be a collection of different available portions of differentphysical storage device locations, such as some available space fromdisks, for example. It will be appreciated that since the virtualvolumes are not “tied” to any one particular storage device, virtualvolumes can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, virtual volumes can include one or more logical unit numbers(LUNs), directories, Qtrees, files, and/or other storage objects, forexample. Among other things, these features, but more particularly theLUNs, allow the disparate memory locations within which data is storedto be identified, for example, and grouped as data storage unit. Assuch, the LUNs may be characterized as constituting a virtual disk ordrive upon which data within the virtual volumes is stored within anaggregate. For example, LUNs are often referred to as virtual drives,such that they emulate a hard drive, while they actually comprise datablocks stored in various parts of a volume.

In one example, the data storage devices 210(1)-210(n) can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumes, atarget address on the data storage devices 210(1)-210(n) can be used toidentify one or more of the LUNs. Thus, for example, when one of thenodes 206(1)-206(n) connects to a volume, a connection between the oneof the nodes 206(1)-206(n) and one or more of the LUNs underlying thevolume is created.

Respective target addresses can identify multiple of the LUNs, such thata target address can represent multiple volumes. The I/O interface,which can be implemented as circuitry and/or software in a storageadapter or as executable code residing in memory and executed by aprocessor, for example, can connect to volumes by using one or moreaddresses that identify the one or more of the LUNs.

Referring to FIG. 3 , node computing device 206(1) in this particularexample includes processor(s) 300, a memory 302, a network adapter 304,a cluster access adapter 306, and a storage adapter 308 interconnectedby a system bus 310. In other examples, the node computing device 206(1)comprises a virtual machine, such as a virtual storage machine. The nodecomputing device 206(1) also includes a storage operating system 312installed in the memory 302 that can, for example, implement a RAID dataloss protection and recovery scheme to optimize reconstruction of dataof a failed disk or drive in an array, along with other functionalitysuch as deduplication, compression, snapshot creation, data mirroring,synchronous replication, asynchronous replication, encryption, etc. Insome examples, the node computing device 206(n) is substantially thesame in structure and/or operation as node computing device 206(1),although the node computing device 206(n) can also include a differentstructure and/or operation in one or more aspects than the nodecomputing device 206(1).

The network adapter 304 in this example includes the mechanical,electrical and signaling circuitry needed to connect the node computingdevice 206(1) to one or more of the client devices 208(1)-208(n) overnetwork connections 212(1)-212(n), which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. In some examples, the network adapter 304 furthercommunicates (e.g., using TCP/IP) via the cluster fabric 204 and/oranother network (e.g., a WAN) (not shown) with cloud storage device(s)236 to process storage operations associated with data stored thereon.

The storage adapter 308 cooperates with the storage operating system 312executing on the node computing device 206(1) to access informationrequested by one of the client devices 208(1)-208(n) (e.g., to accessdata on a data storage device 210(1)-210(n) managed by a network storagecontroller). The information may be stored on any type of attached arrayof writeable media such as magnetic disk drives, flash memory, and/orany other similar media adapted to store information.

In the exemplary data storage devices 210(1)-210(n), information can bestored in data blocks on disks. The storage adapter 308 can include I/Ointerface circuitry that couples to the disks over an I/O interconnectarrangement, such as a storage area network (SAN) protocol (e.g., SmallComputer System Interface (SCSI), Internet SCSI (iSCSI), hyperSCSI,Fiber Channel Protocol (FCP)). The information is retrieved by thestorage adapter 308 and, if necessary, processed by the processor(s) 300(or the storage adapter 308 itself) prior to being forwarded over thesystem bus 310 to the network adapter 304 (and/or the cluster accessadapter 306 if sending to another node computing device in the cluster)where the information is formatted into a data packet and returned to arequesting one of the client devices 208(1)-208(2) and/or sent toanother node computing device attached via the cluster fabric 204. Insome examples, a storage driver 314 in the memory 302 interfaces withthe storage adapter to facilitate interactions with the data storagedevices 210(1)-210(n).

The storage operating system 312 can also manage communications for thenode computing device 206(1) among other devices that may be in aclustered network, such as attached to a cluster fabric 204. Thus, thenode computing device 206(1) can respond to client device requests tomanage data on one of the data storage devices 210(1)-210(n) or cloudstorage device(s) 236 (e.g., or additional clustered devices) inaccordance with the client device requests.

The file system module 318 of the storage operating system 312 canestablish and manage one or more filesystems including software code anddata structures that implement a persistent hierarchical namespace offiles and directories, for example. As an example, when a new datastorage device (not shown) is added to a clustered network system, thefile system module 318 is informed where, in an existing directory tree,new files associated with the new data storage device are to be stored.This is often referred to as “mounting” a filesystem.

In the example node computing device 206(1), memory 302 can includestorage locations that are addressable by the processor(s) 300 andadapters 304, 306, and 308 for storing related software application codeand data structures. The processor(s) 300 and adapters 304, 306, and 308may, for example, include processing elements and/or logic circuitryconfigured to execute the software code and manipulate the datastructures.

The storage operating system 312, portions of which are typicallyresident in the memory 302 and executed by the processor(s) 300, invokesstorage operations in support of a file service implemented by the nodecomputing device 206(1). Other processing and memory mechanisms,including various computer readable media, may be used for storingand/or executing application instructions pertaining to the techniquesdescribed and illustrated herein. For example, the storage operatingsystem 312 can also utilize one or more control files (not shown) to aidin the provisioning of virtual machines.

In this particular example, the memory 302 also includes a moduleconfigured to implement the techniques described herein, as discussedabove and further below.

The examples of the technology described and illustrated herein may beembodied as one or more non-transitory computer or machine readablemedia, such as the memory 302, having machine or processor-executableinstructions stored thereon for one or more aspects of the presenttechnology, which when executed by processor(s), such as processor(s)300, cause the processor(s) to carry out the steps necessary toimplement the methods of this technology, as described and illustratedwith the examples herein. In some examples, the executable instructionsare configured to perform one or more steps of a method described andillustrated later.

FIG. 4 illustrates a system 400 comprising node 402 that implements afile system tier 424 to manage storage 426 and a persistent memory tier422 to manage persistent memory 416 of the node 402. The node 402 maycomprise a server, an on-premise device, a virtual machine, computingresources of a cloud computing environment (e.g., a virtual machinehosted within the cloud), a computing device, hardware, software, orcombination thereof. The node 402 may be configured to manage thestorage and access of data on behalf of clients, such as a client device428. The node 402 may host a storage operating system configured tostore and manage data within and/or across various types of storagedevices, such as locally attached storage, cloud storage, disk storage,flash storage, solid state drives, tape, hard disk drives, etc. Forexample, the storage operating system of the node 402 may store datawithin storage 426, which may be composed of one or more types ofblock-addressable storage (e.g., disk drive, a solid-state drive, etc.)or other types of storage. The data may be stored within storageobjects, such as volumes, containers, logical unit numbers (LUNs),aggregates, cloud storage objects, etc. In an embodiment, an aggregateor other storage object may be comprised of physical storage of a singlestorage device or storage of multiple storage devices or storageproviders.

The storage operating system of the node 402 may implement a storagefile system 418 that manages the storage and client access of datawithin the storage objects stored within the storage 426 associated withthe node 402. For example, the client device 428 may utilize the storagefile system 418 in order to create, delete, organize, modify, and/oraccess files within directories of a volume managed by the storage filesystem 418. The storage operating system may be associated with astorage operating system storage stack 420 that comprises a plurality oflevels through which operations, such as read and write operations fromclient devices, are processed. An operation may first be processed by ahighest level tier (e.g., with lowest latency), and then down throughlower level tiers (e.g., with higher latency) of the storage operatingsystem storage stack 420 until reaching a lowest level tier of thestorage operating system storage stack 420. The storage file system 418may be managed by a file system tier 424 within the storage operatingsystem storage stack 420. When an operation reaches the file system tier424, the operation may be processed by the storage file system 418 forstorage within the storage 426.

The storage file system 418 may be configured with commands, APIs, datastructures (e.g., data structures used to identify block addresslocations of data within the storage 426), and/or other functionality(e.g., functionality to access certain block ranges within the storage426) that is tailored to the block-addressable storage 426. Because thestorage file system 418 is tailored for the block-addressable semanticsof the storage 426, the storage file system 418 may be unable to utilizeother types of storage that use a different addressing semantics such aspersistent memory 416 that is byte-addressable.

The persistent memory 416 provides relatively lower latency and fasteraccess speeds than the block-addressable storage 426 that the storagefile system 418 is natively tailored to manage. Because the persistentmemory 416 is byte-addressable instead of block-addressable, the storagefile system 418, data structures of the storage file system 418 used tolocate data according to block-addressable semantics of the storage 426,and the commands to store and retrieved data from the block-addressablestorage 426 may not be able to be leveraged for the byte-addressablepersistent memory 416.

Accordingly, a persistent memory file system 414 and the persistentmemory tier 422 for managing the persistent memory file system 414 areimplemented for the persistent memory 416 so that the node 402 can usethe persistent memory file system 414 to access and manage thepersistent memory 416 or other types of byte-addressable storage forstoring user data. The persistent memory 416 may comprise memory that ispersistent, such that data structures can be stored in a manner wherethe data structures can continue to be accessed using memoryinstructions and/or memory APIs even after the end of a process thatcreated or last modified the data structures. The data structures anddata will persist even in the event of a power loss, failure and reboot,etc.

The persistent memory 416 is non-volatile memory that has nearly thesame speed and latency of DRAM and has the non-volatility of NAND flash.The persistent memory 416 could dramatically increase system performanceof the node 402 compared to the higher latency and slower speeds of theblock-addressable storage 426 accessible to the node 402 through thestorage file system 418 using the file system tier 424 (e.g., hard diskdrives, solid state storage, cloud storage, etc.). The persistent memory416 is byte-addressable, and may be accessed through a memorycontroller. This provides faster and more fine-grained access topersistent storage within the persistent memory 416 compared toblock-based access to the block-addressable storage 426 through thestorage file system 418.

The persistent memory file system 414 implemented for thebyte-addressable persistent memory 416 is different than the storagefile system 418 implemented for the block-addressable storage 426. Forexample, the persistent memory file system 414 may comprise datastructures and/or functionality tailored to byte-addressable semanticsof the persistent memory 416 for accessing bytes of storage, which aredifferent than data structures and functionality of the storage filesystem 418 that are tailored to block-addressable semantics of thestorage 426 for accessing blocks of storage. Furthermore, the persistentmemory file system 414 is tailored for the relatively faster accessspeeds and lower latency of the persistent memory 416, which improvesthe operation of the node 402 by allowing the node 402 to process I/Ofrom client devices much faster using the persistent memory tier 422,the persistent memory file system 414, and the persistent memory 416.

In order to integrate the persistent memory 416 into the node 402 in amanner that allows client data of client devices, such as the clientdevice 428, to be stored into and read from the persistent memory 416,the persistent memory tier 422 is implemented within the storageoperating system storage stack 420 for managing the persistent memory416. The persistent memory tier 422 is maintained at a higher levelwithin the storage operating system storage stack 420 than the filesystem tier 424 used to manage the storage file system 418. Thepersistent memory tier 422 is maintained higher in the storage operatingsystem storage stack 420 than the file system tier 424 so thatoperations received from client devices by the node 402 are processed bythe persistent memory tier 422 before the file system tier 424 eventhough the operations may target the storage file system 418 managed bythe file system tier 424. This occurs because higher levels within thestorage operation system storage stack 420 process operations beforelower levels within the storage operating system storage stack 420.

The persistent memory tier 422 may implement various APIs,functionality, data structures, metadata, and commands for thepersistent memory file system 414 to access and/or manage the persistentmemory 416. For example, the persistent memory tier 422 may implementAPIs to access the persistent memory file system 414 of the persistentmemory 416 for storing data into and/or retrieving data from thepersistent memory 416 according to byte-addressable semantics of thepersistent memory 416. The persistent memory tier 422 may implementfunctionality to determine when data should be tiered out from thepersistent memory 416 to the storage 426 based upon the data becominginfrequently accessed, and thus cold.

The persistent memory file system 414 is configured with data structuresand/or metadata for tracking and locating data within the persistentmemory 416 according to the byte-addressable semantics. For example, thepersistent memory file system 414 indexes the persistent memory 416 ofthe node 402 as an array of pages (e.g., 4 kb pages) indexed by pageblock numbers. One of the pages, such as a page (1), comprises a filesystem superblock that is a root of a file system tree (a buffer tree)of the persistent memory file system 414. A duplicate copy of the filesystem superblock may be maintained within another page of thepersistent memory 416 (e.g., a last page, a second to last page, a pagethat is a threshold number of indexed pages away from page (1), etc.).The file system superblock comprises a location of a list of file systeminfo objects 404.

The list of file system info objects 404 comprises a linked list ofpages, where each page contains a set of file system info objects. Ifthere are more file system info objects than what can be stored within apage, then additional pages may be used to store the remaining filesystem info objects and each page will have a location of the next pageof file system info objects. In this way, a plurality of file systeminfo objects can be stored within a page of the persistent memory 416.Each file system info object defines a file system instance for a volumeand snapshot (e.g., a first file system info object correspond to anactive file system of the volume, a second file system info object maycorrespond to a first snapshot of the volume, a third file system infoobject may correspond to a second snapshot of the volume, etc.). Eachfile system info object comprises a location within the persistentmemory 416 of an inofile (e.g., a root of a page tree of the inofile)comprising inodes of a file system instance.

An inofile 406 of the file system instance comprises an inode for eachfile within the file system instance. An inode of a file comprisesmetadata about the file. Each inode stores a location of a root of afile tree for a given file. In particular, the persistent memory filesystem 414 maintains file trees 408, where each file is represented by afile tree of indirect pages (intermediate nodes of the file tree) anddirect blocks (leaf nodes of the file tree). The direct blocks arelocated in a bottom level of the file tree, and one or more levels ofindirect pages are located above the bottom level of the file tree. Theindirect pages of a particular level comprise references to blocks in anext level down within the file tree (e.g., a reference comprising apage block number of a next level down node or a reference comprising aper-page structure ID of a per-page structure having the page blocknumber of the next level down node). Direct blocks are located at alowest level in the file tree and comprise user data. Thus, a file treefor a file may be traversed by the persistent memory file system 414using a byte range (e.g., a byte range specified by an I/O operation)mapped to a page index of a page (e.g., a 4k offset) comprising the datawithin the file to be accessed.

The persistent memory file system 414 may maintain other data structuresand/or metadata used to track and locate data within the persistentmemory 416. In an embodiment, the persistent memory file system 414maintains per-page structures 410. A per-page structure is used to trackmetadata about each page within the persistent memory 416. Each pagewill correspond to a single per-page structure that comprises metadataabout the page. In an embodiment, the per-page structures are stored inan array within the persistent memory 416. The per-page structurescorrespond to file system superblock pages, file system info pages,indirect pages of the inofile 406, user data pages within the file trees408, per-page structure array pages, etc.

In an embodiment of implementing per-page structure to page mappingsusing a one-to-one mapping, a per-page structure for a page can be fixedat a page block number offset within a per-page structure table. In anembodiment of implementing per-page structure to page mappings using avariable mapping, a per-page structure of a page stores a page blocknumber of the page represented by the per-page structure. With thevariable mapping, persistent memory objects (e.g., objects stored withinthe file system superblock to point to the list of file system infoobjects; objects within a file system info object to point to the rootof the inofile; objects within an inode to point to a root of a filetree of a file; and objects within indirect pages to point to childblocks (child pages)) will store a per-page structure ID of its per-pagestructure as a location of a child page being pointed to, and willredirect through the per-page structure using the per-page structure IDto identify the physical block number of the child page being pointedto. Thus, an indirect entry of an indirect page will comprise a per-pagestructure ID that can be used to identify a per-page structure having aphysical block number of the page child pointed to by the indirect page.

The persistent memory tier 422 may implement functionality to utilize apolicy to determine whether certain operations should be redirected tothe persistent memory file system 414 and the persistent memory 416 orto the storage file system 418 and the storage 426 (e.g., if a writeoperation targets a file that the policy predicts will be accessedagain, such as accessed within a threshold timespan or accessed above acertain frequency, then the write operation will be retargeted to thepersistent memory 416). For example, the node 402 may receive anoperation from the client device 428.

The operation may be processed by the storage operating system using thestorage operating system storage stack 420 from a highest level downthrough lower levels of the storage operating system storage stack 420.Because the persistent memory tier 422 is at a higher level within thestorage operating system storage stack 420 than the file system tier424, the operation is intercepted by the persistent memory tier 422before reaching the file system tier 424. The operation is interceptedby the persistent memory tier 422 before reaching the file system tier424 even though the operation may target the storage file system 418managed by the file system tier 424. This is because the persistentmemory tier 422 is higher in the storage operating system storage stack420 than the file system tier 424, and operations are processed byhigher levels before lower levels within the storage operating systemstorage stack 420.

Accordingly, the operation is intercepted by the persistent memory tier422 within the storage operating system storage stack 420. Thepersistent memory tier 422 may determine whether the operation is to beretargeted to the persistent memory file system 414 and the persistentmemory 416 or whether the operation is to be transmitted (e.g., releasedto lower tiers within the storage operating system storage stack 420) bythe persistent memory tier 422 to the file system tier 424 forprocessing by the storage file system 418 utilizing the storage 426. Inthis way, the tiers within the storage operating system storage stack420 are used to determine how to route and process operations utilizingthe persistent memory 416 and/or the storage 426.

In an embodiment, an operation 401 is received by the node 402. Theoperation 401 may comprise a file identifier of a file to be accessed.The operation 401 may comprise file system instance information, such asa volume identifier of a volume to be accessed and/or a snapshotidentifier of a snapshot of the volume to be accessed. If an active filesystem of the volume is to be accessed, then the snapshot identifier maybe empty, null, missing, comprising a zero value, or otherwisecomprising an indicator that no snapshot is to be accessed. Theoperation 401 may comprise a byte range of the file to be accessed.

The list of file system info objects 404 is evaluated using the filesystem information to identify a file system info object matching thefile system instance information. That is, the file system info objectmay correspond to an instance of the volume (e.g., the active filesystem of the volume or a snapshot identified by the snapshot identifierof the volume identified by the volume identifier within the operation401) being targeted by the operation 401, which is referred to as aninstance of a file system or a file system instance. In an embodiment ofthe list of file system info objects 404, the list of file system infoobjects 404 is maintained as a linked list of entries. Each entrycorresponds to a file system info object, and comprises a volumeidentifier and a snapshot identifier of the file system info object. Inresponse to the list of file system info objects 404 not comprising anyfile system info objects that match the file system instanceinformation, the operation 401 is routed to the file system tier 424 forexecution by the storage file system 418 upon the block-addressablestorage 426 because the file system instance is not tiered into thepersistent memory 416. However, if the file system info object matchingthe file system instance information is found, then the file system infoobject is evaluated to identify an inofile such as the inofile 406 ascomprising inodes representing files of the file system instancetargeted by the operation 401.

The inofile 406 is traversed to identify an inode matching the fileidentifier specified by the operation 401. The inofile 406 may berepresented as a page tree having levels of indirect pages (intermediatenodes of the page tree) pointing to blocks within lower levels (e.g., aroot points to level 2 indirect pages, the level 2 indirect pages pointto level 1 indirect pages, and the level 1 indirect pages point to level0 direct blocks). The page tree has a bottom level (level 0) of directblocks (leaf nodes of the page tree) corresponding to the inodes of thefile. In this way, the indirect pages within the inofile 406 aretraversed down until a direct block corresponding to an inode having thefile identifier of the file targeted by the operation 401 is located.

The inode may be utilized by the persistent memory file system 414 tofacilitate execution of the operation 401 by the persistent memory tier422 upon the persistent memory 416 in response to the inode comprisingan indicator (e.g., a flag, a bit, etc.) specifying that the file istiered into the persistent memory 416 of the node 402. If the indicatorspecifies that the file is not tiered into the persistent memory 416 ofthe node 402, then the operation 401 is routed to the file system tier424 for execution by the storage file system 418 upon theblock-addressable storage 426.

In an embodiment where the operation 401 is a read operation and theinode comprises an indicator that the file is tiered into the persistentmemory 416, the inode is evaluated to identify a pointer to a file treeof the file. The file tree may comprise indirect pages (intermediatenodes of the file tree comprising references to lower nodes within thefile tree) and direct blocks (leaf nodes of the file tree comprisinguser data of the file). The file tree may be traversed down throughlevels of the indirect pages to a bottom level of direct blocks in orderto locate one or more direct blocks corresponding to pages within thepersistent memory 416 comprising data to be read by the read operation(e.g., a direct block corresponding to the byte range specified by theoperation 401). That is, the file tree may be traversed to identify datawithin one or more pages of the persistent memory 416 targeted by theread operation. The traversal utilizes the byte range specified by theread operation. The byte range is mapped to a page index of a page(e.g., a 4 kb offset) of the data within the file to be accessed by theread operation. In an embodiment, the file tree is traversed todetermine whether the byte range is present within the persistent memory416. If the byte range is present, then the read operation is executedupon the byte range. If the byte range is not present, then the readoperation is routed to the file system tier 424 for execution by thestorage file system 418 upon the block-based storage 426 because thebyte range to be read is not stored within the persistent memory 416. Ifa portion of the byte range is present within the persistent memory 416,then the remaining portion of the byte range is retrieved from thestorage 426.

In an embodiment where the operation 401 is a write operation, accesspattern history of the file (e.g., how frequently and recently the filehas been accessed) is evaluated in order to determine whether theexecute the write operation upon the persistent memory 416 or to routethe write operation to the file system tier 424 for execution by thestorage file system 418 upon the block-addressable storage 426. In thisway, operations are selectively redirected by the persistent memory tier422 to the persistent memory file system 414 for execution upon thebyte-addressable persistent memory 416 or routed to the file system tier424 for execution by the storage file system 418 upon theblock-addressable storage 426 based upon the access pattern history(e.g., write operations targeting more frequently or recently accesseddata/files may be executed against the persistent memory 416).

One embodiment of forwarding operations to bypass persistent memory isillustrated by an exemplary method 500 of FIG. 5 and further describedin conjunction with system 600 of FIG. 6 . The system 600 may comprise anode 601. The node 601 may comprise a persistent memory tier associatedwith persistent memory of the node 601 and a file system tier associatedwith storage managed by the node 601, similar to node 402 of FIG. 4 .The node 601 may implement a persistent memory file system 602 used tostore, organize, and provide access to data within the persistentmemory. The node 601 may implement a storage file system 604 to store,organize, and provide access to data within the storage managed by thenode 601.

In some embodiments, the node 601 may expose a single file system of astorage object (e.g., a volume, an aggregate, etc.) to a client, whosedata is stored across the persistent memory through the persistentmemory file system 602 and the storage through the storage file system604. For example, the node 601 may expose a volume to a client device.Data blocks within the storage of the storage file system 604 may beallocated for the volume. At least some corresponding data blocks may beallocated within pages of the persistent memory by the persistent memoryfile system 602. Some of the data within the storage of the storage filesystem 604 may be copied (tiered) into the persistent memory, and thustwo instances of the data are stored across the storage by the storagefile system 604 and the persistent memory by the persistent memory filesystem 602. Because the persistent memory provides lower latency thanthe storage of the storage file system 604, operations targeting thevolume may be intercepted by the persistent memory tier before reachingthe file system tier. Instead of these operations being implemented bythe storage file system 604 upon the storage, the operations may beimplemented by the persistent memory file system 602 so that clientexperienced latency is reduced.

As operations are executed by the persistent memory file system 602 uponthe persistent memory, data within blocks of the persistent memory maydiverge from data within corresponding blocks of the storage of thestorage file system 604. Accordingly, framing may be performed by thepersistent memory tier to notify the file system tier of blocks withinthe persistent memory that comprise more up-to-date data thancorresponding blocks in the storage of the storage file system 604. Inthis way, the more up-to-date data may be copied from the persistentmemory to the storage of the storage file system 604 and/or certainoperations such as snapshot operations or file clone operations may beexecute in a manner where the more up-to-date data in the persistentmemory will be targeted by such operations as opposed to correspondingstale data within the storage of the storage file system 604.

Because these operations are executed upon the persistent memory by thepersistent memory file system 602 and are not executed by the storagefile system 604 upon the storage, an authoritative copy of data ismaintained within the persistent memory by the persistent memory filesystem 602.

In some instances, certain operations may be more efficient to executethrough the storage file system 604 upon the storage, as opposed tobeing executed through the persistent memory file system 602 upon thepersistent memory. Such operations may correspond to hole punchoperations that free unused blocks of data, partial write operations(e.g., a write to less than a 4 kb block of data, such as where data isappended to an end of file of a file), multi-block sequential writeoperations, and/or certain operations targeting non-tiered data that hasnot been copied from the storage to the persistent memory. It may beadvantageous to forward these operations to the storage file system 604for execution upon the storage and to bypass the persistent memory filesystem 602. This improves the efficiency of executing these operationsbecause the file system tier may more efficiently handle these operationwithout additional complexity that would otherwise be associated withthe persistent memory tier handling these operations. This also ensuresfile system correctness across the persistent memory file system 602 andthe storage file system 604.

Accordingly, as provided herein, forwarding of operations that bypassthe persistent memory file system 602 and are executed by the storagefile system 604 upon the storage may be implemented in a manner thatensures that the authoritative copy of data is to be maintained withinthe persistent memory by the persistent memory file system 602 byremoving stale data from the persistent memory. One or more forwardingpolicies may be defined for when to enable or disable forwarding ofoperations to the storage file system 604.

In some embodiments, a forwarding policy may be defined according to awindow based forwarding mode for a particular file system object, suchas a volume or inode of a file. The forwarding policy may be defined toenable the forwarding of modify operations that target the file systemobject until a forwarding duration timespan of a forwarding durationwindow ends. Modify operations, targeting the file system object duringthe forward duration window and/or satisfying certain criteria, areforwarded to the storage file system 604 for execution upon an instanceof the file system object within the storage of the storage file system604. These forwarded operations will bypass being executed by thepersistent memory file system 602 upon an instance of the file systemobject within the persistent memory. In an example where the forwardingpolicy is implemented during a duration of a snapshot being created by asnapshot creation operation, the criteria may indicate that modifyoperations that would increase a dirty backlog of data to process by thesnapshot creation operation are to be forwarded. In some embodiments,the forward duration window may correspond to a particular amount oftime, a timespan corresponding to execution of an operation (e.g., theforward duration window is in effect until a snapshot operation, a fileclone operation, or some other operation completes), or a triggeringevent occurs.

In some embodiments, if a modify operation has been forwarded to thestorage file system 604 for execution upon the storage of the storagefile system 604 and the forwarding duration timespan has ended after themodify operation being forwarded as the forwarded operation, then theexecution of the forwarded operation is completed through the storagefile system 604 notwithstanding the forwarding duration timespan ending.Once the forwarding duration timespan ends, new incoming operations maybe accepted through the persistent memory tier for potential executionthrough the persistent memory file system 602 upon the persistentmemory.

In some embodiments, a forwarding policy may be defined according to afile block number forwarding mode. Instead of having an establishedforward duration window, any modify operations satisfying a predefinedpolicy are forwarded. In some embodiments, the predefined policy maycorrespond to operations having a hole punch operation type (e.g., anoperation to free an unused block) or a partial write operation type(e.g., an operation writing to a portion of a 4 kb block). In someembodiments, the predefined policy may correspond to operations thattarget non-tiered blocks not maintained within the persistent memoryfile system 602. This is because the non-tiered blocks are locatedwithin block instances of the storage of the storage file system 604 andthere are no corresponding block instances of the non-tiered blockswithin the persistent memory of the persistent memory file system 602.In some embodiments, the predefined policy may correspond to modifyoperations having a multi-block sequential write operation type thatwould be more efficient to execute through the storage file system 604as opposed to through the persistent memory file system 602. Forwardingof these types of operations may improve performance because suchoperations can be more efficiently handled by a storage system layerassociated with the storage file system 604 and/or because execution ofthese operations through the storage file system 604 is more simple andavoids complex interactions that must be dealt with to ensurecorrectness if these operations were otherwise executed by thepersistent memory file system 602.

During operation 502 of method 500 of FIG. 5 , a modify operation 612 towrite new data 618 to a target object may be received by the node 601.In an example, the target object may correspond to a persistent memoryinstance of a file 606 stored within the persistent memory by thepersistent memory file system 602 and may also correspond to a storagefile system instance of the file 608 stored within the storage by thestorage file system 604. The persistent memory instance of the file 606may currently store data 610, which is deemed to be the authoritativecopy of the target object due to the invariant.

During operation 504 of method 500 of FIG. 5 , the modify operation 612and the target object may be compared to a forwarding policy todetermine whether forwarding is enabled for the modify operation 612 andthe target object or whether forwarding is not enabled for the modifyoperation 612 and the target object. During operation 506 of method 500of FIG. 5 , a determination may be made that the forwarding policyindicates that forwarding is not enabled for the modify operation 612and the target object (e.g., a forwarding duration timespan has ended orforwarding is not enabled for the particular target object or operationtype of the modify operation 612). Accordingly, the modify operation 612may be executed through the persistent memory file system 602 upon thepersistent memory instance of the file 606 to write the new data 618 tothe persistent memory instance of the file 606, which is not illustratedby FIG. 6 .

During operation 508 of method 500 of FIG. 5 , a determination may bemade that the forwarding policy indicates that forwarding is enabled forthe modify operation 612 and the target object. Accordingly, the modifyoperation 612 is forwarded 613 to the storage file system 604 as aforwarded modify operation 615 for execution upon the storage filesystem instance of the file 608 and bypasses execution by the persistentmemory file system 602 upon the persistent memory instance of the file606, as illustrated by FIG. 6 . When the storage file system 604receives the forwarded modify operation 615, the forwarded modifyoperation 615 is logged 614 into a log, such as being logged into anon-volatile log (NVLog) of the node 601.

The new data 618 to be written by the forwarded modify operation 615 iswritten 616 to the storage file system instance of the file 608. Oncethe logging is complete 620, a remote direct memory access transfer isperformed. The remote direct memory access transfer transmits anindication to a partner node that is a partner of the node 601 that thenew data 618 has been written into the storage file system instance ofthe file 608, and that the data 610 within the persistent memoryinstance of the file 606 is stale and will be removed from thepersistent memory. The remote direct memory access transfer is performedbecause the partner node maintains a mirrored copy of the data that thenode 601 maintains within the storage of the storage file system 604 andwithin the persistent memory of the persistent memory file system 602.Thus, in the event the node 601 fails and the partner node is to takeover the processing of operations in place of the failed node 601, thepartner node will have up-to-date mirrored data because the partner nodehas or knows to remove corresponding data from a partner persistentmemory of the partner node so that the partner persistent memory of thepartner node mirrors the persistent memory of the node 601.

In some embodiments, once the remote direct memory access transfercompletes 622 and the logging completes 620, the data 610 within thepersistent memory instance of the file 606 is removed 624 because thedata 610 is stale since the new data 618 is now stored within thestorage file system instance of the file 608 and not within thepersistent memory instance of the file 606. In some embodiments, thedata 610 within the persistent memory instance of the file 606 that isstale may be removed before or during the forwarding 613 of the modifyoperation 612 as the forwarded modify operation 615. Removing the data610 within the persistent memory instance of the file 606 that is stalepreserves the invariant that the persistent memory file system 602 is tomaintain the authoritative copy of data that has been copied (tiered)into the persistent memory because the data 610 of the target object isno longer tiered into the persistent memory and has been removed fromthe persistent memory. Once the data 610 within the persistent memoryinstance of the file 606 that is stale has been removed from thepersistent memory, the modify operation 612 may be acknowledged ascomplete to a client that issued the modify operation 612 to the node601.

In some embodiments of determining whether to forward a modifyoperation, a determination may be made that the modify operation spans aplurality of file system objects (e.g., multiple inode of files). If asubset of the plurality of objects satisfies the forwarding policy toenable forwarding, then forwarding is performed for the entirety of themodify operation with respect to the plurality of file system objectseven though some of the plurality of file system objects may not satisfythe forwarding policy to enable forwarding on their own.

Forwarding of operations may have certain interactions with consistencypoint operations being implemented by the node 601, and thus are handledin particular manner to ensure file system consistency and ensure thereis no data loss. Certain modify operations, such as forwardedoperations, may make changes to both the file system tier (the storagesystem layer) such as by writing the new data 618 into the storage filesystem instance of the file 608 and the persistent memory tier such asby removing the data 610 from the persistent memory instance of the file606 that is now stale. A consistency point operation is performed toformally accept these modifications, such as by storing the new data 618to a storage device (flushing to disk).

Once the consistency point operation stores the modifications to thefile system tier (e.g., modifications to data within the storage of thestorage file system 604) to the storage device, the modifications, suchas the new data 618, become part of the storage file system 604 of thefile system tier. In some embodiments, the consistency point operationis performed by the node 601 and the partner node so that themodifications become part of the storage file system 604 of the node 601and a partner storage file system of the partner node. However, if thesemodifications are committed to the storage file system 604 and thepartner storage file system, but the corresponding persistent memorytier changes such as the removal of stale data are left out-of-sync anda crash occurs, then the overall file system may become corrupt because.This is because only modifications to the storage file systems wereimplemented by both the node 601 and the partner node, but themodifications to the persistent memory file systems were not implementedby both the node 601 and the partner node. Accordingly, to ensure acrash does not leave the overall file system corrupt, prior to the filesystem tier committing a modification (e.g., performing a consistencypoint operation to commit the modification such as to write the new data618 to a storage device), the corresponding modifications to thepersistent memory tiers (e.g., removal of stale data, such as the data610) between the node 601 and the partner node are first synchronized.

In some embodiments of synchronizing the changes to the persistentmemory tiers of the node 601 and the partner node, the node 601 may beblocked from implementing a consistency point to flush data from thestorage file system 604 such as the new data 618 to the storage deviceuntil pending remote direct memory access transfers from the node 601 tothe partner node are complete. The remote direct memory access transfersare performed to synchronize the modifications to the persistent memorytiers between the node 601 and the partner node. Once the pending remotedirect memory access transfers are complete and the modifications to thepersistent memory tiers between the node 601 and the partner node aresynchronized, the consistency point may be implemented to commit thechanges to the file system tier, such as to store the new data 618 tothe storage of the storage file system 604. In order to track thepending remote direct memory access transfers from the node 601 to thepartner node, a counter may be maintained to track a count of thepending remote direct memory access transfers. Implementation of theconsistency point operation may be blocked until the count indicatesthat there are no pending remote direct memory access transfers relevantto the consistency point of what modifications are being flushed to thestorage of the storage file system.

One embodiment of forwarding operations to bypass persistent memory isillustrated by an exemplary method 700 of FIG. 7 and further describedin conjunction with system 800 of FIG. 8 . The system 800 may comprise anode 806. The node 806 may comprise a persistent memory tier 808associated with persistent memory 814 of the node 806 and a file systemtier 810 associated with storage 818 managed by the node 806, similar tonode 402 of FIG. 4 and/or node 601 of FIG. 6 . The node 806 mayimplement a persistent memory file system 812 used to store, organize,and provide access to data within the persistent memory 814. The node806 may implement a storage file system 816 to store, organize, andprovide access to data within the storage 818 managed by the node 806.

In some embodiments, the node 806 may expose a single file system of astorage object (e.g., a volume, an aggregate, etc.) to a client device802, which is stored across the persistent memory 814 through thepersistent memory file system 812 and the storage 818 through thestorage file system 816. For example, the node 806 may expose a volumeto the client device 802. Data blocks within the storage 818 of thestorage file system 816 may be allocated for the volume. At least somecorresponding data blocks may be allocated within pages of thepersistent memory 814 by the persistent memory file system 812.

Some of the data within the storage 818 of the storage file system 816may be copied (tiered) into the persistent memory 814, and thus twoinstances of the data are stored across the storage 818 by the storagefile system 816 and the persistent memory 814 by the persistent memoryfile system 812. Because the persistent memory 814 provides lowerlatency than the storage 818 of the storage file system 816, operationstargeting the volume may be intercepted by the persistent memory tier808 before reaching the file system tier 810. Instead of theseoperations being implemented by the storage file system 816 upon thestorage 818, the operations may be implemented by the persistent memoryfile system 812 so that client experienced latency is reduced.

As operations are executed by the persistent memory file system 812 uponthe persistent memory 814, data within blocks of the persistent memory814 may diverge from data within corresponding blocks of the storage 818of the storage file system 816. Accordingly, framing may be performed bythe persistent memory tier 808 to notify the file system tier 810 ofblocks within the persistent memory 814 that comprise more up-to-datedata than corresponding blocks in the storage 818 of the storage filesystem 816. For example, a framing technique may be performed toidentify block within pages of the persistent memory 814 that comprisemore up-to-date data than corresponding blocks within the storage 818 ofthe storage file system 816.

Framing operations, such as framing operation 822, may be transmitted tothe file system tier 810 to notify the file system tier 810 that thecorresponding blocks of the storage file system 816 within the storage818 are stale. The framing operations may comprise file block numbers ofthe blocks within the pages of the persistent memory 814 that comprisethe more up-to-date data. In this way, the file system tier 810 may usethe file block numbers to reference and/or retrieve the blocks withinthe pages of the persistent memory 814, such as to overwrite thecorresponding blocks in the storage 818 of the storage file system 816with the more up-to-date data or to implement various storage operationssuch as snapshot operations or file clone operations that can use thefile block numbers to access the more up-to-date data to include with asnapshot or a file clone.

During operation 702 of method 700 of FIG. 7 , the node 806 may receivea modify operation 804 from the client device 802 at the persistentmemory tier 808. The modify operation 804 may be directed a targetobject to which the modify operation 804 is to write data. An instanceof the target object may be maintained in the persistent memory 814through the persistent memory file system 812 and/or a correspondinginstance of the target object may be maintained in the storage 818 bythe storage file system 816.

During operation 704 of method 700 of FIG. 7 , the modify operation 804and the target object may be compared with a forwarding policy 820 todetermine whether forwarding is enabled for the modify operation 804 andthe target object or is not enabled for the modify operation 804 and thetarget object. In response to determining that the forwarding policy 820specifies that forwarding is enabled for the modify operation 804 andthe target object, the modify operation 804 may be forwarded as aforwarded operation to the file system tier 810 for execution throughthe storage file system 816 upon the corresponding instance of thetarget object within the storage 818.

During operation 706 of method 700 of FIG. 7 , a determination may bemade that there is a pending framing operation such as the framingoperation 822 that is pending to notify the file system tier 810 thatthe instance of the target object within the persistent memory 814 ofthe persistent memory file system 812 comprises more up-to-date datathan the corresponding instance of the target object within the storage818 of the storage file system 816. Accordingly, the forwarded operationthat is to write new data to the corresponding instance of the targetobject within the storage 818 of the storage file system 816 and thepending framing operation that is to notify the file system tier 810that the instance of the target object within the persistent memory 814of the persistent memory file system 812 comprises more up-to-date dataare synchronized so that data loss and/or file system inconsistency doesnot occur. Otherwise, data loss and/or file system inconsistency couldoccur such as where the forwarded operation is executed to write the newdata to the corresponding instance of the target object within thestorage 818 (making the up-to-date data within the persistent memory 814now stale data), and then the pending framing operation is performedsuch that the now stale data may be retrieved and used to overwrite thenew data because the pending framing operation incorrectly indicatedthat the target object within the persistent memory 814 of thepersistent memory file system 812 comprises the more up-to-date data,but actually does not.

In some embodiments of synchronizing the pending framing operation andthe forwarded operation, a determination is made as to whether tosuspend the forwarded operation (e.g., so that the forwarded operationcan be executed after the pending framing operation to ensure the newdata of the forwarded operation is understood to be the more up-to-dateversion of the data) or to cause the pending framing operation to skipthe target object (e.g., so that only the forwarded operation isexecuted to ensure that the new data of the forwarded operation isunderstood to be the more up-to-date version of the data). Thesynchronization may be performed based upon certain internal statesand/or conditions. In an example, in order to perform thesynchronization, internal states, such as metadata, may be maintainedwithin an object, such as by storing the internal states within a memoryin a buffer header for the object (e.g., an internal state may beassociated with a bit mask within a buffer header associated with theobject). This memory may be used to track various internal states, andcan be used to perform the synchronization. In some embodiments, theinternal states and/or conditions correspond to phases through which ablock moves as the block is stored to persistent storage. These phasescorresponds to state transitions of the block as the block makes its wayto the persistent storage, and are tracked as internal statesrepresenting how far along the block is in making its way to thepersistent storage. This state transition data may be stored withinmetadata maintained within memory, such as within a buffer header.

In some embodiments of performing the synchronization, the forwardedoperation may be suspended for subsequent execution after the pendingframing operation based upon a determination that the pending framingoperation is directed to (e.g., currently processing) a subset of fileblock numbers targeted by the forwarded operation. In some embodimentsof performing the synchronization, execution of the framing operation822 may be modified to skip file block numbers targeted by a pendingforwarded operation. In some embodiments of performing thesynchronization, execution of framing operations may be modified to skipfile block numbers that have been forwarded through forwarded operationsand removed from the persistent memory file system 812 while framing wasin progress. For example, there is a framing operation and a forwardedoperation for a same file block number. If the forwarded operationexecutes first, then when the framing operation executes, the framingoperation may be modified to skip the file block number. This is becausethe interleaving forwarded operation has rendered the framing for thisfile block number unnecessary because the forwarded operation nowwritten the newer data to the storage 818 and the framing operationwould otherwise incorrectly indicate that corresponding stale datawithin the persistent memory 814 is more up-to-date.

In some embodiments of synchronizing a consistency point operation andthe forwarded operation, the forwarded operation may be suspended basedupon a file block number targeted by the forwarded operationcorresponding to a dirty block associated with the consistency pointoperation that is to store the dirty block to the storage 818. In someembodiments of implementing the forwarded operation in relation toimplementing consistency point operations, the forwarded operation maytransition from a frame dirty state for a next consistency point to areal dirty state. For example, the forwarded operation might target fileblock number 10 of file (X). Also, there may be a recent framingoperation that executed for this file block number 10 of file (x). Theframing operation would mark file block number 10 as having a framedirty state that is expected to be cleaned (flushed to disk) during anext consistency point, thus the file block number has a “framed dirtystate for a next consistency point.” If this type of object (e.g., fileblock number 10) that has been marked with the “framed dirty state for anext consistency point” is targeted by a forwarded operation, then theforwarded operation is executed to make modifications, and the frameddirty state is overridden with a real dirty state because the filesystem tier 810 (storage system layer) now has real new data to flush todisk.

In some embodiments, a block within the persistent memory file system812 may have a generation count associated with the block. Thegeneration count may be increased each time data of the block is removeddue to the data being stale because to a forwarded operation wrote newerdata to a corresponding block in the storage 818 through the storagefile system 816. A framing operation used to frame the block willinclude the generation count of the block within the persistent memory814, which is compared with a generation count of the correspondingblock within the storage 818 to see if the generation count is stillvalid. In this way, generation counts can be compared to detect invalidgeneration counts such that a framing operation may be modified to skipa file block number, having an invalid generation count, which has beenforwarded and removed from the persistent memory file system 812 whileframing was in progress.

One embodiment of forwarding operations to bypass persistent memory isillustrated by an exemplary method 900 of FIG. 9 and further describedin conjunction with system 1000 of FIGS. 10A and 10B. The system 1000may comprise a node 1004, as illustrated by FIG. 10A. The node 1004 mayimplement a persistent memory file system 1008 used to store, organize,and provide access to data within persistent memory. The node 1004 mayimplement a storage file system 1010 to store, organize, and provideaccess to data within storage managed by the node 1004. In someembodiments, the node 1004 may be partnered with a partner node 1002,such as where the node 1004 and the partner node 1002 are highavailability partners. Accordingly, operations and/or data may bemirrored between the node 1004 and the partner node 1002. For example,the partner node 1002 may locally execute operations, such as modifyoperations, forwarded operations, etc., and replicate 1006 theoperations to the node 1004 that logs the operations into a log 1012(e.g., non-volatile log (NVLog) as operations 1014, as illustrated byFIG. 10A. In this way, during operation 902 of method 900 of FIG. 9 ,the node 1004 may log the operations, executed by the partner node 1002and mirrored/replicated from the partner node 1002 to the node 1004,into the log 1012 as the operations 1014.

During operation 904 of method 900 of FIG. 9 , the node 1004 maydetermine that the partner node 1002 has failed 1020 such as bydetecting a loss of a heartbeat, as illustrated by FIG. 10B. Duringoperation 906 of method 900 of FIG. 9 , the node 1004 may selectivelyreplay 1022 certain operations of the operations 1014 within the log1012. If an operation within the log 1012 is a forwarded operation, thenthe forwarded operation has two part. A first part of the forwardedoperation corresponds to modifying the storage file system 1010 (e.g.,writing new data into the storage of the storage file system 1010). Asecond part of the forwarded operation corresponds to modifying thepersistent memory file system 1008 to remove stale data that was madestale based upon the new data being written into the storage of thestorage file system 1010.

In some embodiments of the selectively replay 1022 of the operations1014 within the log 1012, forwarded operations within the log 1012 arereplayed to modify the storage file system 1010. Forwarded operationswithin the log 1012 are replayed upon the persistent memory file system1008 if the forwarded operations target file block numbers with unknownblock states. Forwarded operations that target file block numbers withknown block states are skipped. In some embodiments, an unknown statemeans that a block is not part of the persistent memory file system1008, and thus the persistent memory file system 1008 has no knowledgeof the block. A known state means that the persistent memory file system1008 tracks the block and owns the block. This ensures file systemconsistency and ensures that there is no data loss. After the operations1014 are selectively replayed 1022 from the log 1012, the node 1004 maycomplete a takeover for the failed partner node 1002 and startprocessing operations in place of the failed 1020 partner node 1002.

Still another embodiment involves a computer-readable medium 1100comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 11 , wherein the implementationcomprises a computer-readable medium 1108, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 1106. This computer-readable data 1106, such asbinary data comprising at least one of a zero or a one, in turncomprises processor-executable computer instructions 1104 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 1104are configured to perform a method 1102, such as at least some of theexemplary method 500 of FIG. 5 , at least some of the exemplary method700 of FIG. 7 , and/or at least some of the exemplary method 900 of FIG.9 , for example. In some embodiments, the processor-executable computerinstructions 1104 are configured to implement a system, such as at leastsome of the exemplary system 400 of FIG. 4 , at least some of theexemplary system 600 of FIG. 6 , at least some of the exemplary system800 of FIG. 8 , and/or at least some of the exemplary system 1000 ofFIGS. 10A and 10B for example. Many such computer-readable media arecontemplated to operate in accordance with the techniques presentedherein.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, in anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on. In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Some examples of the claimed subject matter have been described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the description, forpurposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: receiving, at a persistentmemory tier of a node, a modify operation to write data to a targetobject; in response to a forwarding policy indicating that forwarding isnot enabled for the modify operation and the target object, executingthe modify operation through a persistent memory file system of thepersistent memory tier; and in response to the forwarding policyindicating that forwarding is enabled for the modify operation and thetarget object, forwarding the modify operation as a forwarded operationto a file system tier of the node for execution through a storage filesystem, wherein the execution includes: logging the forwarded operationinto a log of the node; writing the data to the target object within thestorage file system; and in response to the forwarded operation beinglogged in the log, removing a stale copy of the target object from thepersistent memory file system.
 2. The method of claim 1, comprising: inresponse to removing the stale copy of the target object, acknowledgingthe modify operation as complete to a client.
 3. The method of claim 1,comprising: defining the forwarding policy to enable forwarding ofmodify operations targeting the target object until a forwardingduration timespan ends.
 4. The method of claim 1, comprising: inresponse to the forwarding duration timespan ending after the modifyoperation has been forwarded to the file system tier as the forwardedoperation and before completion of the forwarded operation, completingexecution of the forwarded operation through the storage file system. 5.The method of claim 1, comprising: defining the forwarding policy toenable forwarding of modify operations having at least one of a holepunch operation type or a partial write operation type that targetnon-tiered blocks not maintained within the persistent memory filesystem or a multi-block sequential write operation type.
 6. The methodof claim 1, comprising: in response to determining that a first modifyoperation spans a plurality of objects and that a subset of theplurality of objects satisfy the forwarding policy to enable forwarding,performing forwarding for the first modify operation with respect to theplurality of objects.
 7. The method of claim 1, wherein the removing thestale copy comprises: invoking a remote direct memory access transfer toa remote node that is partnered with the node, wherein the remote directmemory access transfer indicates that the stale copy of the targetobject is being removed from the persistent memory file system.
 8. Themethod of claim 1, comprising: blocking the node from implementing aconsistency point to flush data from the storage file system to storageuntil pending remote direct memory access transfers from the node to aremote node are complete.
 9. The method of claim 1, comprising:maintaining a count of the pending remote direct memory access transfersfrom the node to a remote node; and blocking the node from implementinga consistency point to flush data from the storage file system tostorage until the count indicates that there are no pending remotedirect memory access transfers relevant to the consistency point.
 10. Anon-transitory machine readable medium comprising instructions, whichwhen executed by a machine, causes the machine to: receive, at apersistent memory tier of a node, a modify operation to write data to atarget object; determine that a forwarding policy specifies that themodify operation is to be forwarded as a forwarded operation to a filesystem tier of the node for execution through a storage file system; andin response to identifying a pending framing operation that is to notifythe storage file system that more up-to-date data of a block resideswithin a persistent memory file system compared to a corresponding blockwithin the storage file system, synchronize the forwarded operation andthe pending framing operation by either suspending the forwardedoperation or causing the pending framing operation to skip the targetobject.
 11. The non-transitory machine readable medium of claim 10,wherein the instructions cause the machine to: perform a framingtechnique to identify blocks within the persistent memory file systemthat comprise more up-to-date data than corresponding blocks within thestorage file system; transmit framing operations, including the pendingframing operation, to the storage file system to notify the storage filesystem that the corresponding blocks are stale, wherein the framingoperations comprise file block numbers of the blocks comprising the moreup-to-date data; and utilize, by the storage file system, the file blocknumbers to retrieve the more up-to-date data from the blocks within thepersistent memory file system to overwrite the corresponding blocks inthe storage file system.
 12. The non-transitory machine readable mediumof claim 10, wherein the instructions cause the machine to: suspend theforwarded operation based upon a determination that the pending framingoperation is directed to a subset of file block numbers targeted by theforwarded operation.
 13. The non-transitory machine readable medium ofclaim 10, wherein the instructions cause the machine to: suspend theforwarded operation based upon a file block number targeted by theforwarded operation corresponding to a dirty block associated with acurrent consistency point that is to store the dirty block to storage.14. The non-transitory machine readable medium of claim 10, wherein theinstructions cause the machine to: transition the forwarded operationfrom a frame dirty state for a next consistency point to a real dirtystate.
 15. The non-transitory machine readable medium of claim 10,wherein the instructions cause the machine to: modify execution offraming operations to skip file block numbers targeted by a pendingforwarded operation.
 16. The non-transitory machine readable medium ofclaim 10, wherein the instructions cause the machine to: modifyexecution of framing operations to skip file block numbers that havebeen forwarded and removed from the persistent memory file system whileframing was in progress.
 17. The non-transitory machine readable mediumof claim 10, wherein the instructions cause the machine to: compare afirst generation count, maintained by the persistent memory file systemand associated with a framing operation, to a second generation countmaintained by the storage file system for an object targeted by theframing operation to determine whether the first generation count andthe second generation count are valid.
 18. The non-transitory machinereadable medium of claim 10, wherein the instructions cause the machineto: determine whether to suspend the forwarded operation or cause thepending framing operation to skip the target object based upon aninternal state associated with a bit mask within a buffer header of thestorage file system.
 19. A computing device comprising: a memorycomprising machine executable code; and a processor coupled to thememory, the processor configured to execute the machine executable codeto cause the computing device to: log operations, executed by a partnernode and mirrored from the partner node to the computing device, into alog; determine that the partner node has failed; and selectively replaythe operations within the log at the computing device, wherein forwardedoperations within the log are replayed to modify a storage file systemof the computing device, and wherein forwarded operations targeting fileblocks numbers with unknown block states are replayed upon a persistentmemory file system of the computing device.
 20. The computing device ofclaim 19, wherein the machine executable code causes the computingdevice to: during the selective replay of the operations, skip forwardedoperations that target file block numbers having block states within thepersistent memory file system that are known.